Process for separating sodium nitrilotriacetate from a mixture containing the same and sodium chloride

ABSTRACT

1. A PROCESS FOR SEPARATING SODIUM NITRILOTRIACETATE FROM A MIXTURE CONTAINING THE SAME, WHEREIN THE MIXTURE CONTAINS FROM ABOUT 50 TO 85 PERCENT OF SODIUM NITRILOTRIACETATE AND FROM ABOUT 15 TO ABOUT 50 PERCENT BY WEIGHT OF SODIUM CHLORIDE, WHICH CONSISTS IN MAINTAINING AN AQUEOUS SLURRY THEREOF, WHEREIN FROM ABOUT 37 TO ABOUT 47 PERCENT BY WEIGHT IS WATER, AT A TEMPERATURE OF ABOUT +5* TO ABOUT -25*C. FOR ABOUT ONE MINUTE TO ABOUT FIVE HOURS, SEPARATING SOLIDS FROM SAID SLURRY AND THEN RECOVERING A FRACTION RICHER IN SODIUM NITRILOTRIACETATE FROM THE REMAINING LIQUID THAN WAS PRESENT IN THE MIXTURE.

United States Patent Office 3350i Patented Nov. 26, 1974 3,850,984 can be from about 50 to about 85 percent by weight of PROCESS FOR SEPARATING SODIUM NIT O- SNTA and from about 15 to about 50 percent by weight R CE F ROM A MIXTURE CONTAINING of sodium chloride, but generally from about 60 to about THE SAME AND SUDIUM CHLORIDE 80 percent by weight of SNTA and from about 20 to giigg g g gz figzf g ggk gg: i 5 about 40 percent by weight of sodium chloride. The slurry so obtained is maintained at a temperature of about No Drawmg' g kg gg j 184281 +30 to about 30 C., preferably in the range of about s CL 2 0 534 E 3 Claims to about -25 C. for a time sutficient to reach equilibrium, for example, from about one minute to about five hours, preferably from about 15 minutes to about ABSTRACT OF THE DISCLOSURE 10 one hour. Since this process involves a liquid-solids phe- A process for separating sodium nitrilotriacetate from nomenon pressure is of no significance and therefore a mixture containing it and sodium chloride which inatmospheric pressure is preferred. Although relatively volves maintaining an aqueous slurry of the mixture at low temperatures are used herein, no freezing problems a relatively low temperature, separating a fraction rich have been encountered. in sodium chloride from the slurry and then recovering At the end of this time the solids, which are composed a fraction rich in sodium nitrilotriacetate from the remainmainly of sodium chloride and small amounts of SNTA, ing aqueous phase. are separated from the slurry by any suitable means, for M example, by filtration. The filtrate is then treated in any This process is directed to a procedure for recovering Suitable manner to remove water therefrom, for exama fraction predominating in sodium nitrilotriacetate P y heatlhg, leavlhg behind a S011dS raC l H WhlCh (SNTA) from a mixture containing SNTA and sodium 15 composed malnly 0f SNTA Wlth Small amounts of chloride sodium chloride. The composition of the two solids frac- SNTA and sodium chloride can be found in admixture lions Will depend on the composition of the Charge being with each other and the separation of the former from a to a greater eX'EeHt 0n t am u t Of Water used the latter, or the recovery of a mixture predominating in durlhg the exlraetloh m'ost of on the mp SNTA from the original mixture, is often desirable. For tllre used dhl'lhg the extraehoh Procedure SUTPYISiIIgIY, example, SNTA can be prepared by the well-known pro I have found that as the extraction temperature decreases cedure which is exemplified by the following equations: the sehlblhty 0f SNTA 111 Water lnBfeaSeS- The process herein can further be illustrated by the CH8COOH+ClT Hcl'lCICHZCOOH following. Several runs were made wherein water was 3 1CH COOH+NH +6NaOH- added to mixtures of SNTA and sodium chloride to form 3NaCl+SNTA+5H O slurries therewith. After each of the slurries was held at selected temperatures for a period of 15 minutes, the

b h f n tion at a temperature of 100 C. to remove water there- Procedures exemp 1 ed y t e 0 owing aqua 1011s from, leaving behind solids. The filter cake and the solids SNTA-l-HCHNTA (nitrilotriacetic acid) J. from the filtrate were analyzed. The results obtained are NTA+3NaOH- SNTA+3H O tabulated below in Table I.

TABLE I Percent by Weight Filter cake, Filtrate, of SNTA Charge, grams Ml. grams grams remaining H2O Temp, in filter Run number SNTA NaCl added C. SNTA NaCl SNTA NaCl cake 30 20 25 6.3 13.3 23.7 6.7 21 so 20 40 5 3.6 13.4 26.4 6.6 12 a0 20 40 -25 0.3 13.9 29.7 6 1 1 30 20 30 -10 6.9 14.7 23.1 5 s 23 30 20 a0 -25 5.4 15.3 24.6 4 7 1s 40 1o 40 5 7.6 4.7 32.4 5 3 19 4o 10 40 --10 6.8 5.6 33.2 4 4 17 40 10 4o -25 4.4 6.0 35.6 4 0 11 Such recovery is expensive, since it requires additional The advantages of operating under the process defined processing steps and the use of additional chemicals. herein are obvious from the above. It can be seen from I have found that a fraction rich in SNTA can be Runs Nos. 1, 2 and 3 that as the temperature of extracobtained from a mixture containing the same and sodium tion was reduced, unexpectedly the amount of SNTA chloride by the relatively simple procedure of maintaindissolved in the water increased significantly. Even though ing an aqueous slurry of the mixture at a relatively low in the sets of Runs Nos. 4 and 5 and Nos. 6, 7 and 8, temperature, whereby SNTA is selectively dissolved in the the conditions were not optimum, in that less water was water, separating a fraction rich in sodium chloride from present than might be desirable in a commercial embodithe slurry and thereafter recovering a fraction rich in ment, nevertheless, it will be noted that as the extraction SNTA from the remaining aqueous phase. This procedure temperature Was reduced, significantly more SNTA was is eifective because I have found, unexpectedly, that the found in the filtrate. In none of the runs was freezing solubility of SNTA surprisingly increases with decreasing of water noted. If desired, the operation defined herein temperature, can be repeated with the filter cake to selectively remove The process is easily effected. Initially an aqueous therefrom any additional SNTA associated therewith. Alslurry of SNTA and sodium chloride is obtained wherein though in the above runs water was added to the mixabout 25 to about 50 percent by Weight of the slurry, ture of SNTA and sodium chloride to obtain a slurry preferably from about 37 to about 47 percent by weight containing a selected amount of water prior to extracof the slurry is composed of water. The mixture of SNTA tion, it is within the scope of the process to treat slurries and sodium chloride being treated, on a water-free basis, containing SNTA, sodium chloride and water in excess of the amount that is desired to be present during the extraction. In the latter situation, prior to extraction, water in excess of that desired during extraction is removed from the slurry by any suitable means, for example, by evaporation or distillation. The recovered product can be used, for example, as a detergent builder.

Obviously, many modifications and variations of the invention, as hereinabove set forth, can be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A process for separating sodium nitrilotriacetate from a mixture containing the same, wherein the mixture contains from about 50 to 85 percent of sodium nitrilotriacetate and from about 15 to about 50 percent by weight of sodium chloride, which consists in maintaining an aqueous slurry thereof, wherein from about 37 to about 47 percent by weight is water, at a temperature of about +5 to about -25 C. for about one minute to about five hours, separating solids from said slurry and then recovering a fraction richer in sodium nitrilotriacetate from the remaining liquid than was present in the mixture.

2. The process of clam 1 wherein the solids are separated from said slurry by filtration.

3. The process of claim 1 wherein sodium nitrilotriacetate is recovered from said remaining liquid by treating to remove water therefrom.

References Cited OTHER REFERENCES 3,433,832 3/1969 Swanson et a1. 260-534 S 3,183,262 5/1965 Singer et al. 260534 E FOREIGN PATENTS 790,457 2/1958 Great Britain.

OTHER REFERENCES Mullin, Crystallization Butterworths, London (1961) pp. 39-40, 158-159.

N. V. Koninklijke Nederlandse Zoutirdustrie C.A. 53P3557i.

N. V. Koninklijke Nederlandse Zoutindustrie C.A. 54P3887f.

Vogel Practical Organic Chemistry Wiley and Sons (1962), pp. 122-123.

Mullen, Crystallization, Butterworth and Co. (1961), p. 24.

Vogel Practical Oragnic Chemistry, Wiley and Sons (1962), p. 151.

LORRAINE A. WEINBERGER, Primary Examiner J. F. TERAPANE, Assistant Examiner g g UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. ,850,984 Dated November 26, 1974 Inventor(g) Charles M. Selwitz It is certified that error appears in the above-identified patent and that said Letters'Patent are hereby corrected as shown below:

Col. 3, lines 27 and 28, "treating"- ShOL'Ild read ---heating--.

Signed and sealed. this 4th day of February 1975.

(SEAL) Attest:

McCOY MQGIBSON JR. CQ MARSHALL DANN Attesting Officer I Commissioner of Patents 

1. A PROCESS FOR SEPARATING SODIUM NITRILOTRIACETATE FROM A MIXTURE CONTAINING THE SAME, WHEREIN THE MIXTURE CONTAINS FROM ABOUT 50 TO 85 PERCENT OF SODIUM NITRILOTRIACETATE AND FROM ABOUT 15 TO ABOUT 50 PERCENT BY WEIGHT OF SODIUM CHLORIDE, WHICH CONSISTS IN MAINTAINING AN AQUEOUS SLURRY THEREOF, WHEREIN FROM ABOUT 37 TO ABOUT 47 PERCENT BY WEIGHT IS WATER, AT A TEMPERATURE OF ABOUT +5* TO ABOUT -25*C. FOR ABOUT ONE MINUTE TO ABOUT FIVE HOURS, SEPARATING SOLIDS FROM SAID SLURRY AND THEN RECOVERING A FRACTION RICHER IN SODIUM NITRILOTRIACETATE FROM THE REMAINING LIQUID THAN WAS PRESENT IN THE MIXTURE. 